For those of you interested in the exponent of 2 in the kinetic energy formula.....
Let's say you have two steel balls moving frictionless on a plane, they have the same mass (m) but different speeds: v and 2v, and you want to stop them with the same force F.
If you need a time (t) for the one with speed v, then you need a time 2t to stop the one with speed 2v, because V = a*t and a is the same: a = F/m.
Now, why the work you make on the second ball is not 2 times the work you make on the first, but it's 4 times instead?
Work is F*S where S is the space covered. In a constant accelerated motion, S = (1/2)*a*t2 so if time doubles, space becomes 4 times.
So, F is the same but S is 4 times and for this reason the work you have to make to stop the second ball is 4 times the one required for the first.
The work for slide 3 - skateboard problem! Answer with #3 given a height of 3 m .... CHALLENGE (or HW if you did not try last nights HW) try to find all of the values if no height is given, only the fact: the skateboarder is at his maximum height!
Kinetic energy Eureka!
Potential energy Eureka!
For those of you interested in the exponent of 2 in the kinetic energy formula.....
Let's say you have two steel balls moving frictionless on a plane, they have the same mass (m) but different speeds: v and 2v, and you want to stop them with the same force F.
If you need a time (t) for the one with speed v, then you need a time 2t to stop the one with speed 2v, because V = a*t and a is the same: a = F/m.
Now, why the work you make on the second ball is not 2 times the work you make on the first, but it's 4 times instead?
Work is F*S where S is the space covered. In a constant accelerated motion, S = (1/2)*a*t2 so if time doubles, space becomes 4 times.
So, F is the same but S is 4 times and for this reason the work you have to make to stop the second ball is 4 times the one required for the first.
The work for slide 3 - skateboard problem! Answer with #3 given a height of 3 m .... CHALLENGE (or HW if you did not try last nights HW) try to find all of the values if no height is given, only the fact: the skateboarder is at his maximum height!
Phet physics - energy skatepark lab (blank copy)
Phet physics - energy skate park activity and practice problem answers
PE / KE information and practice problems (blank copy)
Answers to PE/KE practice problems
Energy song
REVIEW / EQ answers WITH WORK
How well do you know your PE and KE?!? Take this online quiz to find out.... immediate feedback is available!
http://www.softschools.com/quizzes/science/potential_kinetic_energy/quiz1691.html
Practice Problems (answers listed at the bottom)
Additional practice problems (blank)
Additional practice problem (answers)
21 PRACTICE PROBLEMS FOR CREDIT (ANSWERS):
Lab question - answers: